A new technology that can 3D-print functional human skin might offer an alternative to chemical testing on animals.

Researchers in Madrid created a prototype for a 3D bioprinter that produces a synthetic skin that effectively works the same way as the real thing. Like human skin, it has a top and middle layer, as well as a third layer that consists of fibroblast cells, which produce collagen and gives the printed skin elasticity.

The technology could potentially be used in skin grafts for burn victims, which would require cells from the patient's own skin so the body won't reject it.

It could also be used by cosmetics and pharmaceutical companies to test their products. For these tests, the skin can be printed in large quantities from batches of cells, which could provide a low-cost alternative to animal testing.

Though not required by U.S. law, such tests frequently expose mice, rats, rabbits and guinea pigs to the chemical ingredients in makeup and skin products.

"These can include skin and eye irritation tests where chemicals are rubbed onto the shaved skin or dripped into the eyes of restrained rabbits without any pain relief," Vicki Katrinak, program manager for animal research issues at the Humane Society of the United States, told Seeker.

They also use "skin sensitization tests where test substances are applied to the surface of the skin or injected under the skin of a guinea pig, or applied to the ear of a mouse," she added. "Their skin may show signs of redness, ulcers, scaling, inflammation, and itchiness."

When they're no longer needed, many of the animals used for testing are simply discarded.

"Animals used for testing are usually killed, normally by asphyxiation, neck-breaking or decapitation," Katrinak noted. "Pain relief is not provided."

She explained that there are already many alternative means to test cosmetics that don't involve animals.

"With thousands of ingredients safe for use in cosmetic products and an array of non-animal alternative methods available for use, cruelty-free companies can already create new cosmetics without the need to test on animals," she said.